The U.S. was an early signer of the CISG and ratified it in 1986. In spite of that, the CISG has never been published in any official U.S. treaty source. You should not spend time trying to find the CISG in T.I.A.S. or U.S.T. It is in neither.
The following are good citable locations for the text of the convention:
Probably the most reliable source on the web for the text of the CISG is the website of the United Nations Commission on International Trade Law (UNCITRAL) (opens as PDF).